Field of the Invention
The invention relates to a device for aligning sheets and, more particularly, for feeding sheets with correct registration in sheet-fed rotary printing presses.
It has become known heretofore to provide sheet aligning means, in a forward region of feeding tables at sheet-fed rotary printing presses, for aligning in lateral and circumferential directions a respective sheet conveyed in a sheet stream, before the sheet is transferred to the printing press. In this regard, a sheet transported on the feeding table by a conveyor device is aligned in the circumferential direction at front lays and, thereafter, are drawn up to laterally disposed side stops by side pull marks. The problem often arises that the sheet is slightly twisted or criss-crossed and no longer rests with correct registration at the front lays.
The published German Patent Document DE 42 41 795 A1, for example, discloses a device for feeding sheets to front lays, wherein a cyclically driven drive roller cooperates with a counterpart roller. A sheet passed between these rollers is thus moved cyclically against front lays both before and after the lateral or side alignment has been performed.
It is disadvantageous that means for cyclic driving have to be provided in the device of the foregoing German publication.
A device has become known heretofore from German Patent 839 644 wherein sheets to be aligned are initially transported by means of two parallel conveyor belts in a direction towards front lays and, close to the feed region, are accepted or taken over by a dabbing device formed of a driven lower roller and an upper roller periodically engageable therewith.
The dabbing device is disposed in an extension of the conveyor belts and consequently has the disadvantage that sheets with a format width greater than that dictated by the spacing of the conveyor belts are moved away from the front lay opposite a respective side pulling device, during a lateral alignment by several side pulling devices, so that registration problems can arise in the sheet feeder.